The present invention relates to a multimetallic hydrocarbons conversion catalyst which has the dual-functions of acidity and hydrogenation-dehydrogenation, and the preparation process thereof. In particular, the present invention relates to a multimetallic reforming catalyst comprising platinum and tin and the preparation process thereof.
Catalytic reforming is one of the most important technologies in the petroleum processing, and the main object thereof is to produce gasoline with high octane number, aromatics with wide applications, and hydrogen with low price. At present, the reforming catalysts widely used in industry are mostly bimetallic reforming catalysts such as Ptxe2x80x94Re, Ptxe2x80x94Sn catalysts. It is shown by research that, compared with Ptxe2x80x94Re catalysts, Ptxe2x80x94Sn catalysts have better low pressure stability, and higher aromatics selectivity, have no necessity to be pre-sulfurized, and are more appropriate for moving bed reforming process. The acidity function in the bimetallic catalysts for isomerization is generally provided by porous acidic oxide supports such as alumina and halogens, and the hydrogenation-dehydrogenation function is generally provided by Group VIII metal components such as platinum or palladium. The incorporation of the second metal component, Re or Sn, can greatly improve the stability of the catalyst and reduce the content of the noble metal, platinum.
Several competing reactions take place during the catalytic reforming procedure. These reactions include dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, dehydrocyclization of acyclic hydrocarbons to aromatics, hydrocracking of paraffins to lighter hydrocarbons less than C5, dealkylation of alkylbenzenes, and isomerization of paraffins. In these reactions, the yield of gasoline would decrease due to the formation of light paraffin gases from hydrocracking; the coking reaction would increase the deactivation rate of the catalyst; and the frequent regeneration of the catalyst would increase the operating cost. Therefore, it is always the object of persons skilled in the art to develop a reforming catalyst and process with high selectivity and low carbon deposit rate, wherein the addition of the third or the forth metal component into the bimetallic catalyst is one of the widely used modifying means in the art.
U.S. Pat. No. 3,915,845 discloses a multimetallic catalyst composition for hydrocarbon conversion, comprising 0.01-2.0 wt % of a Pt Group metal, 0.01-5.0 wt % of Germanium, 0.1-3.5 wt % of a halogen and a lanthanide compound, wherein the atomic ratio of lanthanide element/Platinum Group metal is 0.1-1.25. In the catalyst, the Pt Group metal is present as elemental metal state, while the other metals are present as oxide state. The lanthanide elements used are lanthanum, cerium or neodymium.
U.S. Pat. No. 4,039,477 discloses a hydrotreatment catalyst modified with lanthanide metals and the use thereof. Said catalyst comprises a refractory metal oxide, a Pt Group metal, Sn and at least one metal selected from the group consisting of Y, Th, U, Pr, Ce, La, Nd, Sm, Dy and Gd. This patent improves the activity stability of the catalyst by incorporating lanthanide metals into the catalyst and improves the selectivity of the lanthanide-containing catalyst by suppression of the cracking activity due to the presence of tin. In a specific embodiment, the C5+ yield in the conversion of hexanes on a Ptxe2x80x94Snxe2x80x94Ce containing catalyst with a Ce/Pt weight ratio of 0.37 is greater than that of a Ptxe2x80x94Sn containing catalyst.
U.S. Pat. No. 6,059,960 discloses a Ptxe2x80x94Sn multimetallic reforming catalyst containing lanthanide series, wherein the incorporated lanthanide components are Eu, Yb, Sm, or a mixture of Eu and Yb, and more than 50% of the lanthanide metals in the catalyst is a present as EuO. When the composition of the catalyst is Ptxe2x80x94Snxe2x80x94Eu, the relative activity and selectivity are better when the atomic ratio of Eu/Pt is between 1.3 and 2.0. The selectivity of the catalyst will be lowered when said ratio is less than 1.3. The activity of the catalyst will be greatly lowered when the atomic ratio of Eu/Pt is higher than 2.0.
It is an object of the present invention to provide a lanthanide-modified Ptxe2x80x94Sn reforming catalyst with high activity, high selectivity and good activity stability.
It is another object of the present invention to provide a process for preparing the catalyst described above.
The inventors have found that the bimetallic reforming catalyst modified by cerium and europium can improve the selectivity and anti-carbon depositing ability of the catalyst, and thereby increase the liquid yield of the reforming reaction and prolong the lifetime of the catalyst. In particular, the multimetallic catalyst according to the present invention comprises the following components on the basis of mass percents:
Said Group VIII metal is selected from the group consisting of Pt, Pd, to Ru, Rb, Ir, Os or the mixtures thereof, with Pt being preferred. The Group VIII metal component is the major active component of the catalyst according to the present invention. The state of the Pt Group metal present in the catalyst may be an elemental metal or a compound, such as the oxide, sulfide, halide, or oxyhalide, etc., or a chemical combination with one or more other components in the catalyst. The preferred content of the Group VIII metal in the catalyst is 0.05-1.0 mass % on the basis of the elemental metal.
The Group IVA metal in the catalyst is preferably Ge or Sn, more preferably Sn. This metal component may be present as an elemental metal, or as a compound, such as the oxide, sulfide, halide, or oxyhalide, etc., or as a physical or chemical combination with other components of the support and the catalyst. The Group IVA metals preferably are present as an oxide state in the catalyst product. On the basis of elemental metal, the preferred content of the Group IVA metals in the catalyst according to the present invention is 0.1-2.0 mass %.
The lanthanide metals contained in the catalyst according to the present invention are a mixture of Ce and Eu. In the catalyst, Ce and Eu may be present as a compound, such as an oxide, hydroxide, halide, oxyhalide, or aluminate, or as a chemical combination with one or more other components in the catalyst. Each content of Ce and Eu in the catalyst preferably is 0.05-2.0 mass % on the basis of elemental metal, and more preferably 0.1-1.0 mass %. The atomic ratio of Eu/Pt in the catalyst according to the present invention is 0.2-3.0:1, preferably 0.2-1.0:1, more preferably 0.5-1.0:1, and the atomic ratio of Ce/Pt is 0.2-5.0:1, preferably 0.5-3.0:1. More than 60% of Ce in the reduced catalyst is present as the +3 valence.
The component used for adjusting the acid amount in the catalyst according to the present invention is a halogen, preferably chlorine. The content of the halogen in the catalyst is preferably 0.2-4.0 mass %.
Said catalyst support, which is generally a porous adsorptive material and has a specific surface area of 30-500 m2/g, is selected from refractory inorganic oxides. The porous support should have uniform composition 15 and is refractory under the operating conditions. The term xe2x80x9cuniform compositionxe2x80x9d used herein means that the support is not layered and has no concentration gradient of the intrinsic components. If the support is a mixture of two or more refractory materials, these materials have a relative constant content or a uniform distribution throughout the whole support. The refractory inorganic oxides described in the present invention include:
(1) Refractory inorganic oxides, such as alumina, magnesia, chromia, boron oxide, titania, thoria, zinc oxide, zirconia, or the mixtures of the following two oxides: silica-alumina, silica-magnesia, chromia-alumina, alumina-boron oxide, silica-zirconia;
(2) Various ceramics, various alumine, and various bauxites;
(3) Silica, silicon carbide, various synthetic or natural silicates and clays. These silicates and clays may be treated with or without an acid.
In the present invention, the preferred inorganic oxide support is Al2O3, more preferred is the highly pure alumina prepared by the hydrolysis of aluminum alkoxide. The crystalline state of the alumina may be xcex3-Al2O3, xcex7-Al2O3, or xcex8-Al2O3, with xcex3-Al2O3 or xcex7-Al2O3 being preferred. The more preferred crystalline state is xcex3-Al2O3. The alumina powder may be made into various forms such as sphere, sheet, granular, strip, or trefoil.
The aforesaid spherical support can be shaped by the oil-ammonia-drop method or hot oil-drop method. The strip or trefoil support can be prepared by the conventional extrusion shaping method.
The apparent bulk density of said refractory inorganic oxide is 0.4-1.0 g/ml, the mean pore diameter thereof is 20-300 xc3x85, the pore volume thereof is 0.2-1.0 ml/g, and the specific surface area thereof is 100-500 m2/g.
The process for preparing the catalyst according to the present invention comprises separately incorporating the Group IVA metal, Eu, and Ce into the inorganic oxide support, then incorporating an element of the Group VIII metal, preferably Pt. Drying and calcining are needed after each metal component is incorporated.
In the preparation of the catalyst, the Group IVA metal, Eu and Ce should be firstly incorporated, and their incorporation order may be optional. The Group IVA metal may be incorporated firstly, and then Eu and Ce are incorporated, or vice versa. Eu and Ce can be incorporated simultaneously or separately. However, calcination is preferably carried out after each metal component has been incorporated to ensure a firm combination between the incorporated component and the support.
The Group IVA metal component may be incorporated into the catalyst by any means to attain a uniform distribution. Co-precipitation with the porous support, ion exchange, or impregnation may be used for incorporation. The impregnation is to impregnate the support with the solution of a soluble compound of the Group IVA metal and fill or disperse the solution throughout the whole porous carrier material. Suitable soluble compounds of the Group IVA metals are oxides, chlorides, nitrates, or alkoxides thereof such as stannous bromide, stannous chloride, stannic chloride, pentahydrate of stannic chloride; germanium dioxide, germanium tetraethoxide, germanium tetrachloride, lead nitrate, lead acetate, or lead chlorate. Stannic chloride, germanium tetrachloride, or lead chlorate are preferred, since a part of halogens can be incorporated by the above-mentioned chlorides together with the metal components. In addition, the Group IVA metal components can also be incorporated during the preparation of the support.
Cerium and europium in the catalyst can be incorporated in any suitable manner known to those skilled in the art, such as co-precipitation, co-gelation, co-extrusion with the porous support, or ion exchange with the gelled support, etc. The preferred way is to add corresponding hydrated oxides or oxyhalides of cerium and europium and carry out co-gelation or co-precipitation during the preparation of the support, and then dry and calcine the solid. The suitable lanthanum compounds which may form a soluble sol or dispersible sol are lanthanum trichloride or lanthanum oxide.
Another preferred method of incorporating cerium and europium involves utilization of a soluble compound of cerium and europium in solution to impregnate the porous support. The suitable solvents for formulating the impregnation solution comprise alcohols, ethers, acids, wherein inorganic acids such as HCl, HNO3, and the like, organic acids such as oxalic acid, malonic acid, citric acid and the like are preferred. The soluble compounds used for impregnating the support are metal salts, compounds, or complexes of cerium and europium, such as nitrates, chlorides, fluorides, organic alkylates, hydroxides, oxides, wherein cerium nitrate, europium nitrate, cerium chloride, europium chloride, cerium oxide, or europium oxide are preferred. Eu and Ce can be incorporated into the support simultaneously or separately. The incorporation of Eu and Ce can be proceed either before, after, or during the incorporation of the Group VIII metal, preferably after the incorporation of the Group VIII metal.
The Group VIII metals in the catalyst are noble metals components, which can be incorporated into the support in any suitable manner, such as co-precipitation, ion exchange, or impregnation, etc. The preferred method involves the utilization of a soluble, decomposable compound of the Group VIII metals to impregnate the support. The unlimited examples of suitable water-soluble compounds or complexes of the Group VIII metals are: chloro-platinic acid, chloro-iridic acid, chloro-palladic acid, ammonium chloro-platinate, bromo-platinic acid, platinum trichloride, platinum tetrachloride hydrate, platinum dichloro-carbonyl dichloride, dinitrodiamino-platinum, sodium tetranitroplatinate(II), palladium chloride, palladium nitrate, palladium sulfate, diamminepalladium(II) hydroxide, tetramminepalladium chloride, hexamminepalladium chloride, rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate, sodium hexachlororhodate(III), sodium hexanitrorhodate(III), iridium tribromide, iridium dichloride, iridium tetrachloride, sodium hexanitroiridate(III), potassium chloroiridate or sodium chloroiridate, potassium rhodium oxalate. Chlorine-containing compounds of Pt, Ir, Rh, or Pd such as chloro-platinic acid, chloro-iridic acid, chloro-palladic acid, or rhodium trichloride hydrate are preferred. Hydrochloric acid or the like acids such as hydrofluoric acid can be added into the impregnation solution during the process of supporting platinum to facilitate the incorporation of the halogen and the uniform distribution of various metallic components throughout the carrier material. In addition, it is generally preferred to calcined the support after the support has been impregnated with the Group VIII metal in order to minimize the risk of washing away the Group VIII metals in other impregnation steps. The preferred way is to incorporate the Group VIII metal after incorporating other metal components, thus minimizing the loss of the Group VIII metal in other impregnation steps. Generally, the Group VIII metal is uniformly dispersed in the catalyst, or dispersed in the fashion that their concentration gradually decreased from the surface to the center of the catalyst grain.
In each step of the above operation for incorporating the metal component, drying and calcining are necessary after the incorporation of each metal component. The temperature of drying is 25-300xc2x0 C., and the temperature of calcining is 370-700xc2x0 C., preferably 550-650xc2x0 C. Said calcination is generally carried out in an oxygen-containing atmosphere, and the preferred calcination atmosphere is air. The basis for determining the time of calcination is such that most of the metal components in the catalyst are converted to the corresponding oxides. The time of calcination varies with the change of the oxidation temperature and the oxygen content, and it is preferably 0.5-10 hr.
The catalyst according to the present invention can also contain other components or mixtures thereof, which act alone or are combined as catalyst modifiers to improve the activity, selectivity or stability of the catalyst. Said catalyst modifiers include Rh, In, Co, Ni, Fe, W, Mo, Cr, Bi, Sb, Zn, Cd or Cu. These components can be incorporated in any suitable manner into the carrier material during or after the preparation process thereof, or before, after, or during the incorporation of the other components of the catalyst according to the present invention. The content of said modifier is 0.05-5.0 mass %.
The catalyst according to the present invention can also contain alkali or alkali-earth metals, which can be incorporated into the catalyst in any known manner. However, the preferable method is to impregnate the support with an aqueous solution of a water-soluble) decomposable compound of the alkali or alkali-earth metal. Said alkali metals are Cs, Rb, K, Na, or Li, and said alkali-earth metals are Ca, Sr, Ba, or Mg, the content of which is 0.05-5.0 mass %.
The preparation process also comprises a halogen adjustment step to ensure a suitable acidity of the catalyst. The compounds used for incorporating halogens are preferably chlorine, HCl, or an organic compound which can be decomposed to produce chlorine such as dichloromethane, trichloromethane, tetrachloromethane. The temperature of the halogen adjustment is 370-700xc2x0 C., and the time thereof is 0.5-5.0 hr or more. During this procedure, suitable amount of water is required, and the mole ratio of water to HCl is 1.0-150:1. The halogen adjustment step may take place during, or before, or after the calcination of the catalyst. The content of halogen in the final catalyst product is preferably 0.2-4.0 mass %.
It is necessary to employ a reduction step before the use of the catalyst according to the present invention in order to reduce the Group VIII metal component to the corresponding elemental metallic state and to ensure that they are uniformly distributed throughout the refractory inorganic oxide support. The reduction step should be taken place in a substantially water-free environment, e.g., the water content in the reducing gas should be less than 20 ppm. The preferred reducing gas is hydrogen, but other reducing gases such as CO and the like may also be used. The reduction temperature is 315-650xc2x0 C., and the preferred reduction time is 0.5-10.0 hr. The reduction step can be taken place before the catalyst is charged into the reactor, or taken place in situ before the beginning of the reforming reaction.
The catalyst according to the present invention is appropriate for the catalytic reforming of naphtha to increase the octane number of gasoline and the yield of aromatics. Said naphtha is rich in naphthenes and paraffins and selected from full-boiling gasoline having an initial ASTM D-86 boiling point of 40-80xc2x0 C. and an end boiling point of 160-220xc2x0 C., a light gasoline with a boiling range of 60-150xc2x0 C., or a heavy naphtha with a boiling range of 100-200xc2x0 C. Suitable reforming feedstocks are straight run gasoline, partially reformed naphthas, or dehydrogenated naphthas, thermally or catalytically cracked gasoline fraction, and synthetic gasoline.
When the catalyst according to the present invention is used in the catalytic reforming, the absolute pressure is 100 KPa-7 MPa, preferably 350-2500 KPa; the temperature is 315-600xc2x0 C., preferably 425-565xc2x0 C.; the molar ratio of hydrogen/hydrocarbon is 1-20, preferably 2-10; the liquid hourly space velocity (LHSV) is 0.1-10 hrxe2x88x921, preferably 1-5 hrxe2x88x921.
The reforming process must be carried out under a substantially water-free environment. The water content in the feedstock entering into the conversion zone should be less than 50 ppm, preferably less than 20 ppm. The water in the reforming feedstock may be removed by using the conventional adsorbents such as molecular sieves, or be adjusted by suitable stripping operations in a fractionation unit. The water in the feedstock can also be removed by the combination of adsorbent drying and stripping operation. The water content in the hydrogen stream entering into the hydrocarbon conversion zone is preferably 10-20 ppm or less.
The catalyst according to the present invention is also suitable for other hydrocarbon conversion reactions, such as dehydrogenation, hydrogenation, hydrocracking, hydrogenolysis, isomerization, desulfurization, cyclization, alkylation, cracking, and hydroisomerization of hydrocarbon feedstocks.
The catalyst according to the present invention is preferably used in a sulfur-free environment. The desulfurization of the naphtha feedstock can be carried out by any conventional process, such as adsorption desulfurization, catalytic desulfurization, etc. Adsorption desulfurization processes may employ molecular sieves, crystalline aluminosilicates, high surface area SiO2xe2x80x94Al2O3, activated carbon, high surface area metal-containing compounds such as high surface area compounds containing Ni, or Cu and the like. Conventional processes such as hydrorefining, hydrotreating, or hydrodesulfurization and the like can be used for catalytic desulfurization.